radv: emit fmuladd instead of fma to llvm.

radv: emit fmuladd instead of fma to llvm.

For Vulkan SPIR-V the spec states
fma() Inherited from OpFMul followed by OpFAdd.

Matt says the backend will do the right thing depending on the
hardware being compiled for, if you use the fmuladd intrinsic.

Using the Mad Max pts test, on high settings at 4K:
CHP: 55->60
HGDD: 46->50
LM: 55->60
No change on Stronghold.

Thanks to Feral for spending the time to track this down.

Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
Cc: "17.2" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>